Pre-eclampsia is a syndrome of hypertension, edema, and proteinuria that affects 5 to 10% of pregnancies and results in substantial maternal and fetal morbidity and mortality. Pre-eclampsia accounts for at least 200,000 maternal deaths worldwide per year. The symptoms of pre-eclampsia typically appear after the 20th week of pregnancy and are usually detected by the routine monitoring of blood pressure and urine. However, these monitoring methods are ineffective for diagnosis of pre-eclampsia at an early stage, which could reduce the risk to the subject or developing fetus, if an effective treatment were available.
Symptoms of pre-eclampsia generally include any of the following: (1) a systolic blood pressure (BP)>140 mmHg and a diastolic BP>90 mmHg after 20 weeks gestation, (2) new onset proteinuria (1+ by dipstik on urinanalysis, >300 mg of protein in a 24 hour urine collection, or random urine protein/creatinine ratio>0.3), or (3) resolution of hypertension and proteinuria by 12 weeks postpartum. The symptoms of pre-eclampsia can also include renal dysfunction and glomerular endotheliosis or hypertrophy. Other symptoms of eclampsia may be any of the following symptoms due to pregnancy or the influence of a recent pregnancy: seizures, coma, thrombocytopenia, liver edema, pulmonary edema, or cerebral edema.
Pre-eclampsia can vary in severity from mild to life threatening. A mild form of pre-eclampsia may be treated with bed rest and frequent monitoring. For moderate to severe cases, hospitalization is recommended and blood pressure medications or anticonvulsant medications to prevent seizures are prescribed. If the condition becomes life threatening to the mother or the fetus, the pregnancy is terminated and the fetus is delivered pre-term.
Several factors have been reported to have an association with fetal and placental development and pre-eclampsia. They include vascular endothelial growth factor (VEGF), soluble Flt-1 receptor (sFlt-1), and placental growth factor (PlGF). VEGF is an endothelial cell-specific mitogen, an angiogenic inducer, and a mediator of vascular permeability. VEGF has also been shown to be important for glomerular capillary repair. VEGF is disclosed in U.S. Pat. No. 5,332,671; U.S. Pat. No. 5,240,848; and U.S. Pat. No. 5,194,596; as well as in Charnock-Jones et al., 1993, Biol. Reproduction, 48: 1120-1128. VEGF exists as a glycosylated homodimer and includes at least four different alternatively spliced isoforms. The biological activity of native VEGF includes the promotion of selective growth of vascular endothelial cells or umbilical vein endothelial cells and induction of angiogenesis. VEGF includes several family members or isoforms (e.g., VEGF-A, VEGF-B, VEGF-C, VEGF-D, VEGF-E, VEGF189, VEGF165, or VEGF 121); see Tischer et al., 1991, J. Biol. Chem. 266, 11947-11954; Neufed et al., 1996, Cancer Metastasis 15:153-158; U.S. Pat. No. 6,447,768; U.S. Pat. No. 5,219,739; and U.S. Pat. No. 5,194,596. Also known are mutant forms of VEGF such as the KDR-selective VEGF and Flt-selective VEGF described in Gille et al., 2001, J. Biol. Chem. 276:3222-3230. Modified forms of VEGF are described in LeCouter et al., 2003, Science 299:890-893.
VEGF binds as a homodimer to two homologous membrane-spanning tyrosine kinase receptors, the fms-like tyrosine kinase (Flt-1) and the kinase domain receptor (KDR), which are differentially expressed in endothelial cells obtained from many different tissues. GenBank accession number AF063657 provides the nucleotide and amino acid sequences of human Flt-1. Flt-1, but not KDR, is highly expressed by trophoblast cells which contribute to placental formation. PlGF is a VEGF family member that is also involved in placental development. PlGF is expressed by cytotrophoblasts and syncytiotrophoblasts and is capable of inducing proliferation, migration, and activation of endothelial cells. PlGF binds as a homodimer to the Flt-1 receptor, but not to the KDR receptor. Both PlGF and VEGF contribute to the mitogenic activity and angiogenesis that are critical for the developing placenta.
sFlt-1, which lacks the transmembrane and cytoplasmic domains of the full-length Flt-1 receptor, was identified in the culture medium of human umbilical vein endothelial cells and the in vivo expression of sFlt-1 was subsequently demonstrated in placental tissue. sFlt-1 binds to VEGF with high affinity but does not stimulate mitogenesis of endothelial cells. The elevated levels of sFlt-1 found in the serum samples taken from pregnant women suffering from, or at risk of developing, a pregnancy-related hypertensive disorder (e.g., pre-eclampsia or eclampsia) indicate that sFlt-1 is acting as a “physiologic sink” to bind to and deplete the trophoblast cells and maternal endothelial cells of functional growth factors required for the proper development and angiogenesis of the fetus and/or the placenta.